Electro-optical sensors may use Mach-Zehnder interferometers as a method to determine measured voltage signals of a device under test (DUT) in a test and measurement system. It is well known that electro-optic modulators are fabricated using a substrate of electro-optic material by forming an optical waveguide in the substrate and depositing thin film electrodes on the surface of the substrate. When a potential difference is established between the electrodes, an electric field is created within the electro-optic material substrate, and this influences the refractive index of the electro-optic material. Accordingly, when light is propagated through the optical waveguide, its phase and/or magnitude varies in dependence upon the magnitude of the imposed electric field, which provides a measurement mechanism for measuring electrical parameters of the DUT through the electrodes.
Voltage probes based on an electro-optic crystal sensor can be designed to have very high sensitivity and very high input impedance. Often it is desired to have multiple sensitivity ranges in a voltage probe to resolve signals of differing levels. One conventional method to provide for multiple sensitivity ranges is to add a resistive electrical attenuator in the signal path between the DUT and the sensor. The addition of the electrical attenuator in the signal path, however, may reduce the electrical performance and limit the maximum voltages due to power dissipation issues in the attenuator. Such a reduction, when being used with a very high voltage input, has the negative effect of dissipating significant amounts of power through the attenuator.
Embodiments of the invention address this and other limitations of the prior art.